1. Field of the Invention
The present invention relates to annulus pressure responsive downhole tools. Particularly, the present invention provides a low pressure responsive tester valve with a ratchet means operably connecting a power piston to the tester valve.
2. Description of the Prior Art
It is well known in the art that downhole tools such as testing valves, circulating valves and samplers can be operated by varying the pressure of fluid in a well annulus and applying that pressure to a differential pressure piston within the tool.
The assignee of the present invention has recently developed an annulus pressure responsive tool which operates in response to a relatively low annulus pressure increase as shown in U.S. Pat. Nos. 4,422,506 and 4,429,748, both to Beck and assigned to the assignee of the present invention.
These low pressure responsive tools shown in U.S. Pat. Nos. 4,422,506 and 4,429,748 have a power piston which is exposed to well annulus pressure from above, and which has its lower surface exposed to pressurized nitrogen gas in a nitrogen chamber located therebelow. Located below the nitrogen chamber is a metering chamber or equalizing chamber which is filled with oil. A floating piston separates the gas in the gas chamber from the oil in the metering chamber. Disposed in the metering chamber is a metering cartridge which provides a resistance to flow of oil therethrough. The lower end of the metering chamber below the metering cartridge is communicated with well annulus pressure, and a second floating piston separates the oil in the metering chamber from well fluid which enters the lower end of the metering chamber. An increase in well annulus pressure is immediately communicated to the upper surface of the power piston, but is delayed for a significant period of time in being fully communicated to the lower side of the power piston, so that a rapid increase in well annulus pressure will cause a downward pressure differential across the power piston to move the power piston and actuate the tool.
A number of modifications of the basic low pressure responsive tool have been developed by the assignee of the present invention as illustrated in U.S. Pat. No. 4,537,258 to Beck.
One particular feature of such tools to which many of the alternative designs developed by the assignee of the present invention have been directed is the provision of a means for controlling the position of the tester valve during changes in well annulus pressure. That is, while the normal operation of the tool provides for opening and closing of the ball valve in response to reciprocating motion of the power piston, it is sometimes desired to be able to maintain the ball valve in either a closed or an open position during changes in well annulus pressure. There are many reasons for this. For example, it may be desired to run the tool into the well with the ball valve in an open position. Also, it may be desired to pressure test the well annulus after the testing string is in position, without opening the ball valve.
Numerous approaches have been utilized to control the movement of the valve.
Often, an actuating mandrel associated with the valve is initially shear pinned in place to hold the valve closed while running into a well, as shown for example in FIG. 2b of U.S. Pat. No. 4,422,506.
U.S. Pat. No. 4,429,748 to Beck discloses in FIG. 2c thereof a resilient ring assembly 206 to positively control the full opening and closing of the ball valve such that the ball valve is prevented from only partially opening or closing.
U.S. Pat. No. 4,537,258 to Beck discloses several embodiments of such tools. The embodiment disclosed in FIGS. 2A-2E and FIG. 3 thereof utilizes a lug and slot arrangement disposed between the power piston and the housing for controlling movement of the power piston relative to the housing. The embodiment disclosed in FIGS. 5A-5G thereof uses a spring-loaded pin and detent arrangement 600 for locking the actuating mandrel in a position corresponding to an open position of the ball valve.
U.S. Pat. No. 4,355,685 to Beck and assigned to the assignee of the present invention shows a circulating valve having an annulus pressure responsive operating means similar to that of the tools just discussed, and including a lug and slot arrangement disposed between the power piston and the housing as seen in FIG. 1C and FIG. 4 thereof for controlling the position of the power piston relative to the housing.
Another device recently developed by the assignee of the present invention is a multi-mode testing tool shown in U.S. patent application Ser. No. 596,321, filed Apr. 3, 1984, of Ringgenberg. It is noted that application Ser. No. 596,321 itself is not prior art to the present invention; that application is being referred to only as a convenient means for describing one embodiment of the tool shown therein which is a part of the prior art. Application Ser. No. 596,321 shows several embodiments of a ratchet means for operably connecting an actuating mandrel to a power piston, but only the embodiment shown in FIG. 10 thereof is a part of the prior art. The ratchet means disclosed in FIG. 10 of the Ringgenberg application is similar in some respects to the ratchet means utilized in the tester valve of the present invention.